(1) Field of the Invention
The present invention relates to an electrophotographic photosensitive material. More particularly, the present invention relates to an electrophotographic photosensitive material having good ozone resistance, which has excellent initial charge voltage and sensitivity retaining properties when the cycle of charging and light exposure is repeated.
(2) Description of the Prior Art
A photosensitive material comprising an electroconductive substrate and a layer of a photoconductive composition composed of a dispersion of a charge generating pigment (CG) in a charge transporting medium (CT), which is formed on the electroconductive substrate, is used as an electrophotographic photosensitive material having high sensitivity. However, this photosensitive material is defective in that when the reproduction cycle of charging, light exposure, development and toner transfer is repeated, the initial charge voltage and sensitivity are reduced with a relatively small repetition frequency and the life of this material is considerably shorter than that of a selenium photosensitive plate. The reason is considered to be that ozone generated at the charging step or light-excited oxygen generated at the light exposure step attacks the charge generating pigment or medium resin of the photosensitive layer to deteriorate the photosensitive layer.
As means for preventing this deterioration of the photosensitive layer, there has been adopted a method in which a resin having a certain resistance against the attack of oxygen or the like is selected and used for the photosensitive layer. This method, however, is still insufficient in the life of the photosensitive layer, that is, the printing resistance.